Balikpapan would be the last major amphibious operation of World War II. The after-action report for the amphibious operation named Oboe II repeatedly refers to the 18th Infantry Brigade – with some pride – as the ‘assault brigade’. The amphibious assault of Balikpapan would represent the pinnacle of evolution in the Australian infantry brigade from a line infantry formation to an amphibious Infantry Brigade Group (Jungle). The combination of combat experience, administrative efficiency, combined arms capability and leadership would make the 18th Brigade one of the most effective formations the Australian Army fielded in World War II.

Throughout the course of the Pacific War, Australian infantry brigades faced monumental challenges in the SWPA, not only from the terrain and from the enemy but also owing to a rapid evolution of tactics and technologies within these intermediate formations. With time and experience, brigades evolved from rudimentary beginnings into expeditionary forces, incorporating hitherto unfamiliar attached elements, support arms and modes of transportation, all while fighting their way across the SWPA. The Australian infantry brigades adapted from formations established on World War I doctrinal, operational and tactical principles into those using more ‘modern’ organisational techniques and structures. Such an analysis must include a brief examination of the state of these formations at the onset of the war in terms of historical legacies, ‘orders of battle’ and to a limited degree the raw material in terms of manpower represented by Australian brigades at this early stage. One particularly important aspect of this analysis is the key transition of several formations between 1942 and 1945 from ‘standard’ Australian infantry brigades to ‘Infantry Brigade Groups (Jungle)’ and finally to ‘Infantry Brigade Groups (Jungle)’ designated as amphibious ‘Assault Brigades’.2